The long-term goal of this project is to increase our knowledge and understanding of the phonological systems acquired by profoundly deaf children who have used cochlear implants for at least five years. We propose to apply methods from theoretical and clinical linguistics to produce detailed analyses of the phonological systems that underlie speech production by deaf children after cochlear implantation. These detailed linguistic analyses of sound segment inventories, constraints on sequencing, variation in phonetic realizations of morphemes, and implementation of phonological rules will then be compared to both all phonological systems in general and the phonological systems of deaf children who use conventional hearing aids, children who have normal hearing, and fully developed English. Longitudinal analyses of the phonological systems of children who use cochlear implants will identify possible directions and extent of changes in those systems and provide information regarding constraints on changes over time. Subtypes of phonological systems, based on structural similarities, will be identified and related to speech perception abilities and demographic factors such as age at implantation and communication mode to identify specific factors that may affect how phonological systems are structured. This research project will thus address the critical question of how cochlear implants shape the ultimate linguistic systems of children who use them. Findings will provide valuable new empirical and theoretical information about phonological development, which should have important implications for device design, the development and implementation of new intervention programs, and choices in educational placement. Finally, the proposed project on phonological systems of deaf children following cochlear implantation will provide new insights into the ability of the human brain to adapt to electrical hearing as a catalyst for the development of structured linguistic systems underlying spoken language development. [unreadable] [unreadable]